首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   293篇
  免费   13篇
  国内免费   1篇
  2024年   1篇
  2023年   4篇
  2022年   2篇
  2021年   22篇
  2020年   12篇
  2019年   12篇
  2018年   20篇
  2017年   11篇
  2016年   8篇
  2015年   9篇
  2014年   23篇
  2013年   27篇
  2012年   26篇
  2011年   24篇
  2010年   8篇
  2009年   10篇
  2008年   9篇
  2007年   13篇
  2006年   9篇
  2005年   12篇
  2004年   14篇
  2003年   2篇
  2002年   7篇
  2001年   1篇
  2000年   2篇
  1999年   2篇
  1996年   1篇
  1995年   1篇
  1992年   1篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1976年   2篇
  1975年   2篇
  1974年   2篇
  1971年   1篇
  1970年   1篇
  1962年   1篇
排序方式: 共有307条查询结果,搜索用时 15 毫秒
51.

Background

The increasing prevalence of obesity in pregnant women is associated with adverse maternal and neonatal outcomes, and increased costs to healthcare, the economy and broader society.

Objectives

To assess the efficacy of behavioural interventions for managing gestational weight gain (GWG) in the pre-conceptual and pregnancy period in overweight, obese and morbidly obese women.

Search Methods

A search was performed for published studies in the English language, from date? 2000–31 December 2012 in five electronic databases; PubMed, Scopus, Cochrane Library, CINAHL and PsycINFO.

Selection criteria

Studies were included if they compared the efficacy or effectiveness of a particular behavioural intervention in pregnant or pre-conceptual women with standard maternity care. Studies that included women with co-morbid conditions such as diabetes mellitus and polycystic ovarian syndrome were excluded to help isolate the effect of the intervention.

Results

Fifteen studies involving 3,426 participants were included. One study (n = 692) focused on the pre-conceptual period and the remaining 14 (n = 2,734) in the pregnancy period. Pooled mean difference for GWG indicated a lower GWG in the intervention groups when compared to standard maternity care groups (n = 1771, mean difference (MD) −1.66 kg, 95% CI −3.12 to −0.21 kg). With respect to the types of participants, considerable heterogeneity between studies was shown in the obese subgroup [Tau2 = 15.61; Chi2 = 40.80, df = 3 (P<0.00001); I2 = 93%].

Conclusions

Behavioural interventions in pregnancy may be effective in reducing GWG in obese women without comorbid conditions, but not overweight or morbidly obese women. Behavioural interventions had no effect on postpartum weight loss or retention, gestation week of delivery and infant birth weight in overweight, obese and morbidly obese women.  相似文献   
52.
We report a reef ecosystem where corals may have lost their role as major reef engineering species but fish biomass and assemblage structure is comparable to unfished reefs elsewhere around the world. This scenario is based on an extensive assessment of the coral reefs of Farquhar Atoll, the most southern of the Seychelles Islands. Coral cover and overall benthic community condition at Farquhar was poor, likely due to a combination of limited habitat, localized upwelling, past coral bleaching, and cyclones. Farquhar Atoll harbors a relatively intact reef fish assemblage with very large biomass (3.2 t ha−1) reflecting natural ecological processes that are not influenced by fishing or other local anthropogenic factors. The most striking feature of the reef fish assemblage is the dominance by large groupers, snappers, and jacks with large (>1 m) potato cod (Epinephelus tukula) and marbled grouper (E. polyphekadion), commonly observed at many locations. Napoleon wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are listed as endangered and vulnerable, respectively, but were frequently encountered at Farquhar. The high abundance and large sizes of parrotfishes at Farquhar also appears to regulate macroalgal abundance and enhance the dominance of crustose corallines, which are a necessary condition for maintenance of healthy reef communities. Overall fish biomass and biomass of large predators at Farquhar are substantially higher than other areas within the Seychelles, and are some of the highest recorded in the Indian Ocean. Remote islands like Farquhar Atoll with low human populations and limited fishing pressure offer ideal opportunities for understanding whether reefs can be resilient from global threats if local threats are minimized.  相似文献   
53.
54.
The distribution of resistant individuals is determined by the amount of movement between populations. The differential rate of dispersal of a susceptible and a pesticide-resistant strain could influence the resistance dynamics under field conditions. The dispersal rate and dispersal efficiency of the susceptible and propargite-resistant strains of Tetranychus urticae were measured in separate-release and mixed-release experiments. The diffusion coefficient (D) of both strains did not differ significantly (P > 0.344) and an estimate of the asymptotic rate of advance (2  rD) (for one generation) was estimated at 0.1047 and 0.0930 cm per degree day for the susceptible and propargite-resistant strains, respectively. The dispersal efficiency of the two strains differed significantly (P < 0.005) as more susceptible mites than propargite-resistant mites crossed into specified zones more quickly after 290 and 366 degree days. Significantly (P < 0.05) higher number of susceptible adults, immatures and eggs were found in the outer most zone of an arena as compared to that of the propargite-resistant mites. The bioassay of the two strains showed a similar pattern of the spread of the adult females across the specified zones in the mixed-release experiment. The relatively lower dispersive tendency of the propargite-resistant T. urticae and the smaller proportion of adult females exhibiting that behaviour increase the chances of developing resistant ‘hotspots’ in field specially after an acaricide application.  相似文献   
55.
Pierce’s disease (PD) limits the cultivation of Vitis vinifera grape cultivars in California, across the southern United States and into South America. Resistance has been well characterized in V. arizonica, and one resistance locus has been identified (PdR1). However, resistance is poorly characterized in most other grape species. We tested a wide range of Vitis species from the southwestern United States for resistance to PD and used nuclear and chloroplast markers to phenotypically and genetically select a diverse set of resistant accessions. Chloroplast SSR markers identified 11 maternal lineage lines within the set of 17 (14 new and three previously identified) PD resistant accessions. A total of 19 breeding populations (F1 and pseudo-BC1) were developed with the 14 PD resistant accessions, and a total of 705 seedlings were analyzed for PD resistance. Using a limited mapping approach, 12 SSR markers, linked to the PdR1 locus, were used to genotype the breeding populations and phenotypic data were analyzed. Nine accessions had a major resistance quantitative trait locus (QTL) within the genomic region containing PdR1. The phenotypic data for these three resistant accessions, ANU67, b41-13, and T03-16, did not associate with PdR1 linked markers, indicating that their resistance is located in other regions of the genome. These three accessions were identified as candidates for use in the development of framework maps with larger populations capable of detecting additional and unique loci for PD resistance breeding and the stacking of PD resistance genes.  相似文献   
56.
Purpose: This paper aims to summarize recent developments regarding the synthesis, application and challenges of fungal AgNPs. Possible methods to overcome the challenge of synthesis and reduce the toxicity of AgNPs have been discussed.

Materials and methods: This review consults and summary a large number of papers.

Results: Silver nanoparticles (AgNPs) have great potential in many areas, as they possess multiple novel characteristics. Conventional methods for AgNPs biosynthesis involve chemical agents, causing environmental toxicity and high energy consumption. Fungal bioconversion is a simple, low-cost and energy-efficient biological method, which could successfully be used for AgNPs synthesis. Fungi can produce enzymes that act as both reducing and capping agents, to form stable and shape-controlled AgNPs.

Conclusions: AgNPs have great potential in the medical and food industries, due to their antimicrobial, anticancer, anti-HIV, and catalytic activities. However, the observed in vitro and in vivo toxicity poses considerable challenges in the synthesis and application of AgNPs.  相似文献   

57.
58.
Polyhydroxyalkanoates (PHAs) have become an attractive biomaterial in research in the past few years due to their extensive potential industrial applications. Being long chain hydroxyl fatty acid molecules, the PHAs are hydrophobic in nature, and have less functional groups. These features limit their applications in various areas. To enhance their usage, these polymers may need to be modified including surface and chemical modifications. Such modifications may alter their mechanical properties, surface structure, amphiphilic character and rate of degradation to fulfil the requirements for their future applications. Chemical modifications allow incorporation of functional groups to PHAs that could not be introduced through biotechnological methods. These chemically reformed PHAs, with enhanced properties, could be used for broad range of applications. This review aims to introduce different chemical modification approaches including some recent methods that had not been explored or discussed so far for PHAs as possible technologies for widening the range of product and application potentials. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:29–41, 2018  相似文献   
59.
60.
Poly(A) Binding Protein Nuclear 1 (PABPN1) is a multifunctional regulator of mRNA processing, and its expression levels specifically decline in aging muscles. An expansion mutation in PABPN1 is the genetic cause of oculopharyngeal muscle dystrophy (OPMD), a late onset and rare myopathy. Moreover, reduced PABPN1 expression correlates with symptom manifestation in OPMD. PABPN1 regulates alternative polyadenylation site (PAS) utilization. However, the impact of PAS utilization on cell and tissue function is poorly understood. We hypothesized that altered PABPN1 expression levels is an underlying cause of muscle wasting. To test this, we stably down-regulated PABPN1 in mouse tibialis anterior (TA) muscles by localized injection of adeno-associated viruses expressing shRNA to PABPN1 (shPab). We found that a mild reduction in PABPN1 levels causes muscle pathology including myofiber atrophy, thickening of extracellular matrix and myofiber-type transition. Moreover, reduced PABPN1 levels caused a consistent decline in distal PAS utilization in the 3’-UTR of a subset of OPMD-dysregulated genes. This alternative PAS utilization led to up-regulation of Atrogin-1, a key muscle atrophy regulator, but down regulation of proteasomal genes. Additionally reduced PABPN1 levels caused a reduction in proteasomal activity, and transition in MyHC isotope expression pattern in myofibers. We suggest that PABPN1-mediated alternative PAS utilization plays a central role in aging-associated muscle wasting.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号